Cracks in deck plating in way of deck penetrations of oil tankers has been an increasing problem and is typical on vessels with high strength steel in deck and most typically found on Buoy loading Oil Tankers trading in the North Sea. The damaged areas (as shown in this post) were limited to cracks in the upper deck plating in way of the pipe penetrations resulting in small leaks, but could easily have resulted in more serious damage to the deck structure and the safety of the ship if left unattended over time.

The semi-submersible “flotel” (floating hotel) Alexander L. Kielland capsized on 27 March 1980 while bridge connected to the steel jacket Ekofisk Edda platform. The flotel lost one of its five legs in severe gale force winds, but not an extreme storm. The accident started with one of the bracings failing due to fatigue, thereby causing a succession of failures of all bracings attached to this leg. It was discovered during the investigation that the weld of an instrument connection on the bracing had contained cracks, which had probably been in existence since the rig was built. The cracks had developed over time, and the remaining steel was less than 50%.

During survey of cargo centre tanks, cracks were found in some of the deck longitudinals in a amidships. The cracks had penetrated through the flange, into the web of the deck longitudinal, and further into the deck plating at one location. The most probable cause of the cracking was fatigue due to longitudinal hull girder stresses combined with unfavourable location of welding in a knuckle.